Blender: Exporting a large 3D map into a 2D image
Blender's ability to render large images is pretty robust: We do images 10Kx10K and larger all the time, so your viewport view is not a limiting factor.

Set up your camera to view the entire map, either overhead or however you wish to see the map inside your final 2D image. Set Blender's render dimensions to something large enough to accomplish your readability goals. This could easily be many thousands of pixels in either or both dimensions. Hit render.



You may want to experiment with camera settings to get the best image possible. Also, remember that if you are using an image texture within the 3D map (say, a 1024 x 1024 image as a ground texture), Blender cannot magically render it 20K x 20K without pixelization.  We use 4K skins and higher when we are working on big images... If procedural textures accomplish what you need, you'll have no problems.

Hope this helps... big images are a real strength of Blender, and shout if I can assist.